netdev - Re: [PATCH net-next 3/6] cnic: Fix panic in cnic_iscsi_nl_msg

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Message-ID: <20100226184001.GJ6733@linux.vnet.ibm.com>
Date:	Fri, 26 Feb 2010 10:40:01 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Michael Chan <mchan@...adcom.com>
Cc:	"'Simon Horman'" <horms@...ge.net.au>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 3/6] cnic: Fix panic in
	cnic_iscsi_nl_msg_recv() when device is down.

On Thu, Feb 25, 2010 at 11:01:59PM -0800, Michael Chan wrote:
> Simon Horman wrote:
> 
> > On Wed, Feb 24, 2010 at 04:42:06PM -0800, Michael Chan wrote:
> > > Some data structures are freed when the device is down and it will
> > > crash if an ISCSI netlink message is received.  Add RCU protection
> > > to prevent this.  In the shutdown path, ulp_ops[CNIC_ULP_L4] is
> > > assigned NULL and rcu_synchronized before freeing the data
> > > structures.
> >
> > Is rcu_assign_pointer() unnecessary in cnic_cm_open()?
> > It doesn't seem to be followed by rcu_synchronized() and the pointer
> > doesn't seem to be accessible anywhere else at that time.
> 
> We assign a valid pointer in cnic_cm_open() so that it can be used
> during run-time (in service_kcqes() for example).  During shutdown in
> cnic_stop_hw(), we assign NULL followed by rcu_synchronize().

So you are saying that when the pointer is assigned in cnic_cm_open(),
there cannot possibly be any concurrent reading threads?

Use of an explicit rcu_assign_pointer() would be better if so.

							Thanx, Paul
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